Water-absorbent resins have found wide use in a variety of applications, including sanitary goods, hygienic goods, water retaining agents, dehydrating agents, sludge coagulants, condensation preventing agents and release control agents for various chemicals. Water-absorbent resins are available in a variety of chemical forms including substituted and unsubstituted natural and synthetic polymers such as hydrolysis products of starch-acrylonitrile graft polymers, carboxymethylcellulose, crosslinked polyacrylates, polyvinyl alcohols, polyacrylonitrile, polyvinylpyrrolidones, sulfonated polystyrenes, hydrolyzed polyacrylamides and polyethylene oxide.
Each type of water-absorbent resin differs in ease and cost of manufacture, chemical and physical properties, rate of water absorption, and degree of water absorption and retention, thus making the ideal water-absorbent resin a difficult composition to find. For example, the hydrolysis products of starch-acrylonitrile graft polymers have a comparatively high ability to absorb water, but require a cumbersome process for production and have the disadvantages of low heat resistance and decaying or decomposing easily due to the presence of starch. Conversely, other water-absorbent polymers are easily and cheaply manufactured and are not subject to decomposition, but do not absorb liquids as well as the starch-acrylonitrile graft polymers.
Therefore, it would be extremely advantageous to provide a method of increasing the water absorption properties of a stable, easy to manufacture water-absorbent resin to match the superior water absorption properties of a difficult to manufacture polymer. Likewise, it would be advantageous to increase the liquid absorption properties of an already superior water-absorbent resin.
Any method of improving the water absorption properties of the resin must also retain the "dry feel" of the resin after liquid absorption. Although water and liquid absorption is the primary function of the water-absorbent resin, in many applications it is almost equally important that the polymer maintain its "dry feel". The polymer must be able to absorb amounts of water several times its weight, plus be sufficiently crosslinked to avoid partial solubilization of the polymer to form a gel and lead to a slippery, wet feeling. Presently, water-absorbent polymers do possess a "dry feel" after significant water absorption, thus any methods directed to improving the water-absorbent properties of the resin should not alter the basic "dry feel" after liquid absorption.
Any treatment of a water-absorbent resin both increasing the water absorption capabilities and maintaining its basic "dry feel" would enhance and broaden the application possibilities of many water-absorbent polymers. Such a treatment should be simple and economical to avoid increases in the raw material cost or manufacturing cost of the basic polymer.